1. Field of the Invention
The invention relates to systems of X-ray diagnosis and, more particularly, to systems used for the angiographic examination of the lower limbs. It also relates, in such systems, to a device that enables the tracking of the movement of a contrast medium or embolus and the taking of radiographic pictures in synchronism with said movement.
Angiography is the technique of X-ray diagnosis applied and adapted to the vascular system: namely the arteries, veins and perfused tissues. It makes use of iodine-based liquids, known as contrast liquids, that are opaque to X-rays. These liquids are injected into the vascular system in order to enable its display by differentiation with respect to the surrounding tissues. More precisely, the patient is stretched out on a table that is designed, for example, so as to move under a source of X-radiation associated with a receiver positioned on the other side of the patient from the source. In other systems of X-ray diagnosis, the table is fixed while the assembly consisting of the radiation source and receiver is movable. The practitioner injects a dose of contrast medium into an artery or vein of the patient stretched out on the table. Then, some seconds after this injection, he takes several successive radiographic shots of the patient so as to display the blood vessels and measure the progress in time of the dose of contrast medium, also called an embolus, in said blood vessels.
When the angiographic examination is limited to a part of the body that corresponds to the field of the receiver, namely to the dimensions of the radiographic film or of the radiological image intensifier, the pictures are made without moving the patient, namely the table, in relation to the source/receiver assembly or vice versa.
For angiographic examinations that concern the lower limbs, namely a length of about 120 centimeters, there are three methods used at present.
A first method consists in the use of a radiographic film of great length so as to cover the totality of the lower limbs in a single shot and take several successive shots, for example six of them, separated by time intervals that enable the progress of the contrast medium to be recorded. For each shot, the entire surface of the lower limbs is irradiated, thus leading to high exposure to X-rays. This is detrimental to the patient and entails a relatively high cost due to the price of large-format radiographic films. Furthermore, the number of shots available in the devices generally used is limited, usually to six. This means that the taking of the shots has to be spaced out in anticipating the progress of the contrast medium as efficiently as possible. Finally, an unnecessarily large part of the patient is irradiated since several images are made before or after the contrast medium reaches each point. This means that the time of passage of the contrast medium has to be lengthened and hence that, in order to preserve the same concentration, the volume injected has to be increased. This may be harmful to the patient, owing to the toxicity of the product, and may increase the cost of the examination.
A second method consists in examining the lower limbs zone by zone, each zone corresponding, for example, to a useful field of 35 cm .times. 35 cm or to a diameter of 30 or 35 cm. To this end, a first injection of contrast medium is made, and several successive shots are taken of the zone close to the injection. Then, the table or the source/receiver assembly is shifted to center the images on a neighboring zone. The same operations, namely the injection of the contrast medium and the recording of the images, can then be started again. The process is then recommenced in its entirety for the following zones. Thus, each series of shots of a zone makes it possible to see the passage of the contrast medium in the circulatory system of said zone from start to finish. Such a method leads to the carrying out several injections (in practice, as many injections as there are positions and radiographed zones): this takes time, results in considerable discomfort for the patient, and is costly in terms of contrast medium. Finally, this method leads to a great number of exposures and the result thereof is an additional irradiation of the patient and an increase in the cost of the examination when the receiver is constituted by a radiographic film.
A third method consists in carrying out a single injection of the contrast medium and in making a relative shift between the patient and the source/receiver assembly so that the part of the patient facing the source/receiver assembly is constantly the part where the concentration of contrast medium in the circulatory system enables the making of the desired images of this product. This third method calls for optimum synchronization, for the shifting operations, between the successive positions of the shots and the passage of the contrast medium. At present, the radiology tables designed for this type of examination have a selection of forward motions in fixed steps and at constant time intervals, the duration of which is left to the practitioner's discretion. They do not provide the practitioner with easy control over the examination stages which would enable him to follow the progress of the contrast medium irrespectively of the field of the receiver, the morphology of the patient and the pathological aspects of the case.
The foregoing description of the three methods of angiographic examination shows that the problem of determining the progress of the contrast medium along the circulatory system of the lower limbs is common to all three of them, even if the consequences are critical in varying degrees depending on the method considered.
A known way of following the passage of the contrast medium is for practitioners to use the patient's reactions and/or sensations during the passage of the contrast medium, for example sensations of heat, discomfort or pain, so that the taking of the different shots is matched in real time with the progress of the contrast medium.
An object of the present invention, therefore, is to make a device for the detection of the progress of the contrast medium that requires neither the patient's cooperation nor the same degree of attention on the practitioner's part.
Another object of the present invention is also the making of a system of X-ray diagnosis for angiographic examinations, that includes a device such as this to detect the progress of the contrast medium so as to synchronize the taking of the different shots with the position of the contrast medium detected by said device.
The invention is based on the observation that the contrast medium, through its composition in organic salts tri-substituted by iodine atoms, prompts reversible physiological modifications related to the concentration of contrast medium in the blood at the place concerned. The effect of the contrast medium may be expressed briefly and schematically, with respect to the invention, by the notion of vasodilatation of the blood vessels. This vasodilatation occurs in such a way that the result thereof is an in increase in the peripheral circulation of blood through the expansion of the small vessels. This phenomenon is propagated as and when the contrast medium moves on. It is this property that shall be turned to advantage in the contrast medium detection devices according to the present invention.